This invention relates to the monitoring of the concentration of the .components of a dope used in the manufacture of cellulose fibre and other cellulose product from a solution of cellulose in an organic solvent, particularly an amine oxide solvent and water. Cellulose manufactured in this manner is known as lyocell and Will hereafter be referred to as solvent-spun cellulose or lyocell. The term "dope" as used herein refers to the solution of cellulose in an aqueous tertiary amine oxide.